Volume control



Jan. 16, 1945. w. R. KocH VOLUME coNT'RL Filed June 1 5, 1942 .M b e ,/0Mw Www/Q W/ m m f H www 6 0 f v 7W? wfg n a j 4 731 a m Nm EN 0M PGJ TMWn l SmJAentor Bg Gttorneg j uma ..1-

Partnr ifi y2,367,357 voLUMa con'rnor.

winnen n. noch, nemmeno, N. Radio Corporation of America,

` of Delaware 3., assignor to a corporation Application .lune 15, 1942,Serial No. 447,009 '9 Claims. (Ci. 179-171) My present invention relatesto volume controls for radio receivers, and more particularly to amanually-adjustable volume control device mum battery drain. The usualmethods of gain control, applied to an audio amplifier stage forexample, are undesirable.. Grid bias control produces distortion; audioinput level control engenders maximum battery drain.

Accordingly, it may be stated to be one of the main objects of mypresent invention to provide a method ofL and means for, securing volumereduction in a portable receiver of the battery type with minimumbattery drain; the method employing' concurrent degenerative feedback toimprove iidelity.

Another important object of my invention is to provide an audio ampierwhose output energy level is regulated by varying the screen voltagethereof thereby to provide distortionless and eiiicient volume control.

Another important object of my invention is to provide a volume controlfor a signal amplifier, which control varies the positive voltage of apositive auxiliary electrode; operation of the control subsequent tominimum volume'position resulting in actuation of an on-o switchtorender the amplifier ineffective.

Yet another object of my invention is to provide in a battery-operatedportable receiver a manual volume control which simultaneously variesscreen vvoltage and eects variable degeneration thereby to improvefidelity with minimum battery drain.

Still other objects are to improve generally the efiiciency andsimplicity of battery-operated portable receivers.

'I'he novel features which I believe to be characteristic of myinvention are set forth with particularity in the appended claims; theinvention itself, however, as to both its organization and method ofoperation will best be understood by reference to the followingdescription taken in connection with the drawing .in which I haveindicated diagrammatically a circuit organization whereby my inventionmay be carried into effect.

Referring, now, to the drawing, there is shown a rectangle designatedPortable receiver. It

` amplifier tube I and its associated circuits.

signal input grid 3,.

end of arm I0 .is grounded, while the free end t. The signal gridresistor of a demodulator, or to the plate load of a prior l tudes.,They have common is to be understoodthat Awhile my invention hasapplication to various types oi receivers portable or non-portable,nection with diminutive portable receivers of the battery-operated type.Such. flciently compact to fit into a .vest pocket; the batteries are,therefore, small and current drainage is an important factor in design.Such receivers have a self-contained signal pick-up device, as, forexample, a loop. usually a crystal ear-phone reproducer ofthe type usedin deaf-aid apparatus.

' In the drawing I have only shown the audio The tube I has a iilament2, a a screen grid a suppressor grid 5 and a plate 3 may be coupled tothe load audio amplier. The coupling condenser 1 acts to couple the grid3 to the prior stage; grid return resistor 8 connects grid 3 to ground.The battery'for energizing the tube is denoted by numeral 9.

The battery is divided into two sections. One of these is the A sectionfor heating the lament 2. The other section '1s the B section forsupplying the plate and screen voltages for tube I. The negativeterminal of battery 9 is grounded through the spring metal switch armI0. The xed contact Il is directly connected to the minus terminal ofbattery 9. The fixed of the arm I0 is provided with an insulation studI2. The switch I I-III is the on-cir" switch of amplier tube I, and,hence, of the entire receiver. The plate 6 is connected to the posi`tive terminal of batteri,rv 9 through a path comprising the choke coilI3 and lead I4. One terminal of the filament 2 is grounded, while theother terminal is connected to the positive terminal of the A section ofbattery 9. Leads I5 may be connected to filaments of prior tubes so thatthe A section of ments of all the receiver tubes.

The screen grid 4 is connected to the lower end of choke coil I3 bymeans of an adjustable rheostat arm I 6. The rheostat' comprises aplurality of resistors Il,` I8 and I9. These resistors are arranged inthe order of increasing magniterminals connected to the screen grid 4,while the opposite terminals are adapted to be successively Vcontactedby arm I6 for thevolume control adjustment function. An additionalcontact point 2li is connected directly with. the screen "grid so thatwhen the it has especial utility in con-- receivers are suf- Thereproducer is battery 9 heats the'laf volume control is at position20-I6 the volume vlevel of the receiver is maximum. When the arm I 6 isadjusted to connect resistor II in the screen circuit the volume isreduced. As the arm 20 is further adjusted successively to connect therespective resistors I8 and I9 into circuit with the screen grid, thevolume level is still further reduced. When resistor I9 is in circuitwith the screen grid, then the volume level is a minimum. Merely by wayof illustration,it is pointed out that resistor I'I may have a magnitudeof 0.2 megohm; resistor I8 mayf have a value of 1 megohm; while resistorI9 may have a value of 10 megohms.

Upon adjusting arm I6 in a counter-clockwise sense from the minimumvolume position, the

free end of arm I6 will open switch Il-IU due to pressure againstinsulation stud I2. Hence, when the contact arm I6 is in position suchas to contact stud I2, the receiver will be in off condition. Thoseskilled in the art are fully acquainted with the manner of constructingan on-olf switch so that when arm I6 is adjusted to open switch II-IU,the latter will remain fixed in that position until it is actuated toincrease the volume.

A condenser 30 connects the screen grid 4 to ground, and acts to bypasscurrents of high audio frequencies from .the degenerative path; thelatter path is provided by the successive resistors inserted in thescreen grid circuit. The anode choke coil I3 will prevent rapid decreaseof gain at low audio frequencies when the volume control arm I6 isadjusted to decrease the volume level. 4,Audio voltage developed acrossthe plate load is transmitted through the coupling condenser 40 to thecrystal reproducer. It will be noted that one terminal `of the crystalreproducer is connected to the ungrounded end of resistor 4 I, while theother terminal is connected to the grounded end of the resistor.

Capacitor 4l serves to block direct current from the crystal reproducer.However, any leakage through this 'capacitor might charge up thecapacitor formed by the crystal reproducer. Resistor 4I bypasses anysuch leakage current. By grounding the lower end of the crystalreprodiicer, the shock hazard to the listener is reduced. Furthermore,audio currents owing through the cathode-anode path in the tube Icomplete their circuit through the crystal reproducer, thus keep- Yprevents the negative feedback from being as effective for high audiofrequencies as for the middle register. Therefore, as theivolume controlis adjusted toward'the minimum volume position, the amplification of themedian audio fresired, or when a strong signal tends to overload theoutput tube. By inserting a variable resistor in the screen circuit ofthe final audio amplifier tube, reduced volume can be, secured byreducing the screen voltage. At the same time the screen resistorvintroduces a negative feedback for audio frequencies thereby to reduceany distorticn caused by the amplifier tube. By combining the on-olfswitch with the minimum volume control position zero volume is readilysecured. Because the filaments heat very rapidly, this system forobtaining zero output level is satisfactory.

tion of distortion quencies is reduced faster than that of the higherand lower audio frequencies. In actual tests made on this circuit, itwas found that on a` strong local station, with reduced volume controlsetting, the screen voltage on the tube was only 10 volts instead of theapplied plus 45 volts.

The negative feedback action occurs in the following manner. Byinserting a resistor in the screen circuit audio frequency voltagesappear across the inserted resistor. The electrons reaching the plate 6are, therefore, affected by two grids. These grids are the control grid3 and the screen grid 4. The voltages of these two grids are inopposition. That is, when grid 3 is at the positive peak of the audiocycle, the screen grid 4 will be most negative. If a sine wave isapplied to grid 3, and the tube is not linear, the voltage appearing ongrid 4 will be non-sinusoidal, and of such shape as to correct for thenon-linearity of the portion getting through to the plate. Thus, thelarger kthe magnitude of the resistor inserted in circuit with grid 4,the larger is the negative feedback effect and the less will be theaudio gain through the tube. Of course, instead of the tapped type ofswitch shown in the screen grid circuit, a continuously variableresistor may be employed for finerv control.

While I have indicated and described a system for carrying my inventioninto effect, it will be apparent to one skilled in the art that myinvention is by no meansY limited to the particular organization shownand described, but that many modifications may be made without departingfrom the scope of my invention, as set forthin the appended claims.

What I claim is:

1. A method of operating a signal amplifier of r the type including ascreen grid tube which includes applying signals to said tube, derivingampliiied signal energy from the tube, varying the direct currentvoltage of solely the screen grid of the tube to control the signaloutput level thereof, and concurrently developing signal voltage in thescreen circuit of the tube which is in degenerative phase with thesignals applied to the tube thereby to reduce distortion caused by theamplifier.

2. A method of operating a signal amplier of the type including a screengrid tube which includes applying signals to said tube, derivingamplified signal energy from the tube, varying the direct currentvoltage of solely the screen grid of the tube, `concurrently developingsignal voltage in the screen circuit of the tube which is indegenerative phase with the signals applied to the tube, andconcurrently varying the screen grid voltage and said degenerativevoltage magnitude in opposing senses to control the lev'el of saidamplifiedsignals with simultaneous reduccaused by the amplifier.

3. In a portable receiver of the battery-operated type, an amplifierprovided with at least a cathode. signal grid, screen grid and plate,means for applying 'audio signals to the signal y grid, a battery forprovidingpositive potentials of said screen which is in degenerative i2,367,357 t for said screen grid. and plate, arbattery for enervariableresisterl is capable of providing a variable degree of degeneration ofaudio Isignal voltage throughout the range ot .itsadjustment 4. In aportable receiver of the battery-operated type, an ampliiler providedwith at least a cathode, signal grid, screen grid andv plate, means forapplying audio signals' to the signal grid, Aa battery for providingpositive potentials for said screen grid and plate, a battery forenergizing the cathode to emit electrons, variable resistor meansconnected inV circuit with said first battery and screen grid forvarying the effective positive voltage of the screen grid, said viding avariable degree of degeneration of audio signal voltage throughout therange of its adjustment, and means, responsive to adjustment gridvoltage variation means, for rendering the second battery ineiiective toenergize said cathode at the minimum positive voltage setting of saidvoltage varying means.

5. The method of reducing the gain of an elec- -tronic ampliiler havinga filament, at least two grids, andan anode, and in which the electronstream is modulated by a si grid; which includes reduc on of amplitudeoi the modulated electron stream by opposing signal voltages on thesecond grid obtained by consecutively connecting resistances ofincreasing values between solely the second grid and a point on thevoltagev supply positive with respect to said lament, and thereafterinterrupting current to said filament.

6. Annethod of operating a signal ampliiier of the type including a'screen grid tube which inc ludes applying signals to said tube,deriving am,- -signai energy from the-tube, developing signal voltage inthe screen circuit of the tube, varying the direct current voltage ofsolely the screen grido! the tube, and concurrently varying the signalvoltage in 'the screen circuit of the tube phase with the signalsapplied to the tube. l

7. A method of operating an audio signal am'-plifierofthetypeincludingascreengridtube which lincludes applying audiosignals to said tube, deriving amplified audio signal energy fromthetube,varyingthedirectcurrent voltag'eof variable resistor DTO-f alimpressed on one s control the level of said lamplied audio signals.

8. Ina portable receiver of the batteryoper' i to reduce illament signalgrid, screen grid i in response to reduction of plate current therebysolely thescreen grid of the tube, developing audio voltage in thescreen circuit of the tube which is in degenerative phase with the audiosignals applied to the tube, and concurrently varying the screen gridvoltage and said degenerative voltage magnitude in opposing senses toated typ'e, an ampliiler provided with at least a and plate, signals tothe signal providing positive potentials means for applying audio grid,-a battery for iory said screen grid ergizing the filament to emitelectrons, variable resistor means connected in circuit with said firstbattery and screen gri( for varying the eiiective positive voltage ofthe screen grid, saidvariable resistor providing a variable degree ofdegeneration of audio signal voltage throughoutthe range of itsadjustment, and 'means responsive toadjustment of said variable resistorto minimum volume setting for interrupting current to said filament.

9.' Ina portable receiver of the battery-operated type, an audioamplifier tube provided with at least a cathode, signal grid, screengrid and plate, means for applying audio signals to the signal grid, abattery for providing -positlve potentials for said screen grid andplate, means for energizing the cathode to emit electrons, variableresistor means connected in circuit with said ilrst battery and screengrid for decreasing the efiective positive voltage of the screen gridthereby the tube gain with small battery drain, said -variable resistorproviding a variable degree of degeneration of audio signal voltagethroughout the range of its adjustment, a capacitor operativelyassociated with said variable resistor for preventing degeneration frombeing as eifective for high audio frequencies as for median audiofrequencies, a coil in circuit between the plate and a desired point ofthe battery. saidcoil having developed thereacross amplified audiosignal voltage, said coil having an increase in inductance to improvethe low audio frequency response relativeto median laudio frequencies.and means, responsive to adjustment of said screen grid voltagevariation means, for rendering thecathode energizing means ineilectiveto energize said cathode' at the minimum positive voltage setting ofsaid voltage varying means.

WINFIIEIDR..KOGH.v

and plate, a battery for en-

